引言

Spring Cloud是微服务开发的全家桶。本文介绍其核心组件和应用。

一、服务注册与发现（Eureka）

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// Eureka Server
@EnableEurekaServer
@SpringBootApplication
public class EurekaServerApplication {
    public static void main(String[] args) {
        SpringApplication.run(EurekaServerApplication.class, args);
    }
}

// application.yml
server:
  port: 8761
eureka:
  client:
    register-with-eureka: false
    fetch-registry: false
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// Eureka Client
@EnableEurekaClient
@SpringBootApplication
public class ServiceApplication {
    public static void main(String[] args) {
        SpringApplication.run(ServiceApplication.class, args);
    }
}

// application.yml
spring:
  application:
    name: user-service
eureka:
  client:
    service-url:
      defaultZone: http://localhost:8761/eureka/

二、服务调用（Feign）

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@FeignClient(name = "user-service")
public interface UserClient {
    @GetMapping("/users/{id}")
    User getUser(@PathVariable Long id);
}

@RestController
public class OrderController {
    @Autowired
    private UserClient userClient;
    
    @GetMapping("/orders/{id}")
    public Order getOrder(@PathVariable Long id) {
        User user = userClient.getUser(id);
        // 业务逻辑
        return order;
    }
}

三、API网关（Gateway）

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@SpringBootApplication
public class GatewayApplication {
    public static void main(String[] args) {
        SpringApplication.run(GatewayApplication.class, args);
    }
}

// application.yml
spring:
  cloud:
    gateway:
      routes:
        - id: user-service
          uri: lb://user-service
          predicates:
            - Path=/api/users/**
          filters:
            - StripPrefix=1
        - id: order-service
          uri: lb://order-service
          predicates:
            - Path=/api/orders/**

四、配置中心（Config）

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// Config Server
@EnableConfigServer
@SpringBootApplication
public class ConfigServerApplication {}

// Config Client
@SpringBootApplication
public class ServiceApplication {
    @Value("${my.config}")
    private String config;
}

// bootstrap.yml
spring:
  cloud:
    config:
      uri: http://localhost:8888
      name: application
      profile: dev

五、熔断器（Resilience4j）

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@Service
public class UserService {
    @Autowired
    private UserClient userClient;
    
    @CircuitBreaker(name = "userService", fallbackMethod = "fallback")
    public User getUser(Long id) {
        return userClient.getUser(id);
    }
    
    public User fallback(Long id, Exception e) {
        return new User(id, "Default User");
    }
}

// application.yml
resilience4j:
  circuitbreaker:
    instances:
      userService:
        failure-rate-threshold: 50
        wait-duration-in-open-state: 10s

总结

Spring Cloud核心组件：

  1. Eureka：服务注册与发现
  2. Feign：声明式HTTP客户端
  3. Gateway：API网关
  4. Config：配置中心
  5. Resilience4j：熔断降级

参考资料